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Preparation Techniques

Preparation Techniques. Solid Freeform Fabrication Foams Method Starch consolidation (*) Gel-casting Dual phase mixing Burn-out of organic phases (*) Polymeric sponge method (*). * Used at our Dept. One of the polymers of glucose…. Starch as pore former

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Preparation Techniques

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  1. Preparation Techniques • Solid Freeform Fabrication • Foams Method • Starch consolidation (*) • Gel-casting • Dual phase mixing • Burn-out of organic phases (*) • Polymeric sponge method (*) * Used at our Dept.

  2. One of the polymers of glucose… • Starch as pore former • Insoluble in water at low T, but swelling occurs

  3. Starch form a gel in contact with water and turn a ceramic suspension into a rigid body • After burn-out of starch and sintering of the ceramic matrix, a material is obtained with porosity corresponding to the swollen starch particles

  4. Polveri ceramiche (mm) H2O distillata Amido (mm) Preparazione sospensione Miscelazione e riscaldamento Gelificazione Posizionamento in stampo Consolidamento Burn-out Sinterizzazione OVERALL SCHEME OF PREPARATION

  5. Starting material (SCNM) 50%SiO2 - 16% CaO - 25% Na2O - 9% MgO Powders sieved < 106mm

  6. b) a) c) Several types of starch

  7. a) potato mais rice 25% weight

  8. 15 % starch Poor porosity 30% starch Bad sintering

  9. A GOOD MATERIAL HAS… • Average Porosity 100 mm • Total porosity 40%vol. • Res. Compression 6 MPa

  10. Confronto tra SNCM tal quale, dopo 15 gg SBF e dopo 1 mese SBF SNCM 1 mese SBF SNCM 15 gg SBF SNCM polvere Comparison between original material and after soaking in SBF 2 weaks in SBF Development of HAp 4 weaks in SBF

  11. Preparation Techniques • Solid Freeform Fabrication • Foams Method • Starch consolidation (*) • Gel-casting • Dual phase mixing • Burn-out of organic phases (*) • Polymeric sponge method (*) * Used at our Dept.

  12. An ORGANICCOMPONENT occluded into the matrix leaves POROSITY in the ceramics when burnt away. Polymers used: PMMA, PE and PEG. The organic component must be homogeneously dispersed and removed without damaging the ceramic structure

  13. Starting materials • Glass powders SCK (SiO2-CaO-K2O) • Polyethylene with suitable size METHOD • Mixing glass powder and polyethylene • Uniaxial compression • Thermal Treatament

  14. Uniaxial pressing Disks and bars

  15. Two types of PE with different grain saize PE1: 100-300mm PE2: 300-600mm

  16. Conditions of Treatment 950°C 3h Differential thermal analysis: 3 crystallization peaks: at 950°C only one left

  17. Vetroceramic material (amorphous matrix + one or more dispersed crystalline phases)

  18. NEEDS • Maximize % vol. porosity • Sufficient dimensions of pores • Satisfactory mechanical properties • Establish highest tolerable PE content

  19. MERCURY POROSIMETRY Mercury does not wet the solid

  20. PROCEDURE • Outgassing of the sample and filling with Hg. • Initial pressure due to the height of the column • Increase in pressure causes Hg intrusion into smaller and smaller pores • Max achievable pressure dictates smallest measurable diameter • Results: total pore volume, Plot of pore distribution

  21. Washburn equation: inverse relationship between pressure and pore radius • = surface tension of mercury • θ = contact angle between Hg and the • sample

  22. Porosimetry results for (PE1-50) Small pores between 1 - 6mm Large pores round 85 mm

  23. Total pore volume for three samples from the same batch Good reproducibility Pore volume larger than that of PE: additional porosity due to evolution of gases during burning out

  24. Other means to study porosity: analysis of SEM images

  25. SEM back-scattering Different coloration according to pore size

  26. 35 30 30 25 20 Numero pori 15 11 10 5 4 3 0 50-100 100-200 200-300 300-650 Dimensioni pori [micron] Distribution of pores according to size. Big pores (useful for vascularization) and small pores (useful in cellular adhesion)

  27. Volume of pores as a function of size

  28. Good interconnection of porosity Trabecular porosity

  29. Behavior of scaffolds in SBF

  30. 48h in SBF High bioactivity 7 days in SBF

  31. 2 weaks in SBF

  32. Glass material more soluble than corresponding vetroceramic

  33. Scaffold, with very high surface, has a weight loss much more pronounced! (30% after 3 months)

  34. Processes: • release of cations (K+) • capture of H+ from solution • Increase in pH (up to 9: non compatible with a successful implant).

  35. Vetroceramic: good adhesion of osteoblasts after 6h

  36. Cellular death after 4 days, due to an increase in pH!)

  37. POSSIBLE SOLUTION Pre-treatment in SBF before implant to quench the pH change • ADVANTAGES • Avoid cellular death • Implant a material with HAp microcrystals already present: better osteointegration

  38. Proliferation on scaffold after pre-treatment in SBF: marked increase in cellular response

  39. The end

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